I know that some people while walking through the dark streets are holding house keys in their fist. It is meant to incerase damage inflicted on hypothetical agressor face. Something like improvised knuckle-duster.

Can it really improve one's defence capability? I think it gives you just a little bit of momentum. Moreover it hurts your palm during impact.

To sum up: Is it better to punch someone with keys placed inside your fist or without them?

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I think the idea is not to hold them in your fist but hold them so the keys protrude between your fingers... which gives a much greater force/area ratio when used for striking (more penetration).
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kbelderJun 2 '14 at 17:29

4 Answers
4

First, unless you have trained punching people with keys in between your fingers, the result will be as much (if not more) damage to yourself as with the target. You may drop your keys as a result of the impact and pain which means that you lost your keys. Punch Injuries: Insights into Intentional Closed Fist Injuries provides some interesting reading on people getting injured while punching.

Second, I am not a lawyer nor do I play one on TV, however if you go into a situation with intend to inflict harm with an object then that object might be viewed as a weapon. Thus, you might be arrested and charged under with assault. If you are concern about this, speak with your criminal attorney.

Third, in almost all civilian self defence situations, it is better to not be there instead of fighting. Make sure you are not in a position to be assaulted. If you are, run to safety as soon as you can.

This. I worked in an ER, and I've seen a few injuries where the webbing between the fingers was shredded, keys embedded in palms, etc. Also, in many countries assault is merely the threat, battery is the act of striking. It can be compounded as you say, by wielding anything that appears to be a weapon.
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JohnPJun 3 '14 at 14:25

As it mentions in the comments, the idea is to have the keys protrude from within your fingers so that you can scratch someone. I personally would not do this. There are reasons for this:

It takes a bit of time to setup. If I am attacked, it will probably be without warning, therefore I will not be able to get my keys between my fingers in time. If I knew I might be attacked, for example, walking in a part of town I shouldn't, I would be able to set up a much better defense, for example, a knife.

It will only tick the bad guy off, even if you do manage a good shot. Unless you get a key directly in someone's eye, it's not going to do much (in which case you could have used your fingers). Keys may cut if you apply enough force, but they are not sharp like a knife. They will not make you into an impromptu Wolverine.

I don't like to load my fist with anything. I know there are martial artists who advocate this, but in the styles I practice, a well-formed (tight) fist is preferred. I haven't noticed an increase in force from experimenting with a loaded fist. If I was going to load my fist, I would do so with something solid like a Kubotan rather than something that will shift and hurt my hand like a handful of keys.

Sorry you didn't get the physics answer you were looking for, but hopefully this practical answer helps you out. I would recommend a Kubotan (and learning how to use it) over a handful of keys any day.

There's basically two ways to use a normal set of keys for self defense.

1. Between the knuckles

Held protruding between the knuckles you might be able to get a gouge on someone, particularly in the eyes, neck or cheek. The problem is that you have to hold it in such a way that the keys do not slide back into your hand while you're doing it, and it often depends on how you have your keys set up.

My suggestion for anyone doing this would be to actually play with it and try stabbing cardboard to see if you can hold up under resistance to your force.

2. Between forefinger and thumb... as a key

This is more done as a classic knife/shiv/shank move, and again, the targets are going to be the same. You've got a slightly better grip in this case, and a lot more target control. The method would be stab then twist.

Obviously, if you've got something sharper, like mini-scissors, screwdriver, or wine bottle corkscrew, that works better.

Is it effective?

Well, obviously if you can have a better weapon, you should probably use that instead. Gouging with a not-entirely-sharp object might cause enough pain to dissuade them, but if they're ramped up enough on adrenaline, if they're not feeling pain, if they've got on heavy clothing protecting a lot of targets... it's not exactly the best choice.

I recommend small 5-7 inch maglites or the bar section of a U-lock as better choices for non-weapon weapons. Sharp objects are theoretically more deadly, but the problem is how well trained are you in using them, and, of course, does that really make sense given your self defense laws and needs? Mostly, clubbing someone in the head/face with an object and stunning them enough for you to run away is what most folks need in civilian situations.

Punching with vs. without

I do a knife art, so I'd be comfortable using it if I had to, but... I also have stuff better than keys on my keychain to use instead. For most folks, I'd say practice with stabbing cardboard and see how well it holds in your hand, how well you can maintain your grip and how well you can target. If you can't, stick to what you can use effectively.

I have seen some horrific photos of injuries sustained from trying to put the keys between the knuckles where they slipped from impact. Try putting keys in your key and push them up against a hard surface. Notice that it doesn't take much pressure before they twist and start pushing into your flesh. Holding a key between thumb and forefinger is a bit better, but it's really only good for raking at the eyes and forehead (a cut to the forehead has a decent chance of blinding them with the copious blood flow, plus it really hurts). Ideally, you're better off running, but if someone runs up and scoops you up, a quick rake to the face can convince them to drop you so that you can run.

That said, if you can form a proper fist, you're better off just punching with that. Better, you can get a kubotan to attach with your keys, which gives you a punching weight, a flail, and a joint manipulation stick all in one. That said, be warned that it may be considered a weapon and confiscated wherever weapons are not allowed (airports, federal buildings, etc). They're also a bit awkward to stuff in your pocket at first.